Abstract
Maladaptation is widespread in natural populations. However, maladaptation has most often been associated with absolute population decline in local habitats rather than on a spectrum of relative fitness variation that can assist natural populations in their persistence at larger regional scales. We report results from a field experiment that tested for relative maladaptation between‐pond habitats with spatial heterogeneity and (a)symmetric selection in pH. In the experiment, we quantified relative maladaptation in a copepod metapopulation as a mismatch between the mean population phenotype and the optimal trait value that would maximize mean population fitness under either stable or fluctuating pH environmental conditions. To complement the field experiment, we constructed a metapopulation model that addressed both relative (distance from the optimum) and absolute (negative population growth) maladaptation, with the aim of forecasting maladaptation to pH at the regional scale in relation to spatial structure (environmental heterogeneity and connectivity) and temporal environmental fluctuations. The results from our experiment indicated that maladaptation to pH at the regional scale depended on the asymmetry of the fitness surface at the local level. The results from our metapopulation model revealed how dispersal and (a)symmetric selection can operate on the fitness surface to maintain maladaptive phenotype–environment mismatch at local and regional scales in a metapopulation. Environmental stochasticity resulted in the maintenance of maladaptation that was robust to dispersal, but also revealed an interaction between the asymmetry in selection and environmental correlation. Our findings emphasize the importance of maladaptation for planning conservation strategies that can support adaptive potential in fragmented and changing landscapes.
Highlights
Our study addresses knowledge gaps in expectations for the frequency and persistence of population maladaptation from phe‐ notype–environment mismatch in relation to spatial structure and environmental fluctuations (Laine, 2004; Lemoine et al, 2012; Tack et al, 2014)
We report results from a common garden field experiment and from a metapopulation model that tested for the existence of an asymmetric fitness to low phenotype × selection (pH) in copepod populations and pre‐ dicted its importance for the maintenance of total regional mal‐ adaptation to pH in relation to spatial structure and environmental fluctuations
Similar to results obtained in another study (Marshall et al, 2010), we found that maladaptive phenotype–environment mismatch was maximal when selection occurred over spatial scales that are much smaller than dispersal distance
Summary
Evolutionary principles are increasingly considered in the conser‐ vation of fragmented populations (Carroll et al, 2014; Hendry et al, 2011). Much of this focus has been on conditions that promote local adaptation as in for example stable or growing populations (e.g., Kawecki & Ebert, 2004; Kirkpatrick & Barton, 2006; Yeaman, 2015; Hoban et al, 2016). Less focus has been placed on malad‐ aptation, in which population fitness is suboptimal and declining (Brady et al, 2019; Crespi, 2000; Hendry & Gonzalez, 2008). This is despite that maladaptation has the potential to influence meta‐ population dynamics in fragmented habitats (Farkas, Mononen, Comeault, & Nosil, 2016; Marshall, Monro, Bode, Keough, & Swearer, 2010; Nicolaus & Edelaar, 2018). Studies that have explicitly sought to establish expectations for the frequency and persistence of maladaptation in natural systems in relation to spatial structure and environmental fluctuations are rare (Laine, 2004; Lemoine, Doligez, & Richner, 2012; Tack, Horns, & Laine, 2014)
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